diff --git a/slides/cours_21.md b/slides/cours_21.md
index 18e4d0d6fe65acf0db5b884ad30c5f3e927d433a..327ded0846c05f1d3b7996274682146175340196 100644
--- a/slides/cours_21.md
+++ b/slides/cours_21.md
@@ -483,8 +483,8 @@ matrice arbre_à_matrice(arbre)
 
 ```C
 void qt_to_matrix(node *qt, int nb_li, int nb_co, int matrix[nb_li][nb_co])
-    for (int li = 0; li < nd_li; ++li) {
-        for (int co = 0; co < nd_co; ++co) {
+    for (int li = 0; li < nb_li; ++li) {
+        for (int co = 0; co < nb_co; ++co) {
             node *current = position(li, co, qt);
             matrix[li][co] = current->info;
         }